The goal of this proposal is to improve the efficacy of adrenoviral liver directed gene therapy in the Gunn rat animal model of congenital non- hemolytic unconjugated hyperbilirubinemia. Crigler-Najjar syndrome type I, familial non-hemolytic jaundice and kernicterus, is a fatal disease which can potentially be cured by genetic complementation. The disease results from a genetic defect in the enzyme responsible for glucuronidation of bilirubin. In its severest form, bilirubin accumulates in the serum leading to kernicterus and death. One feature of this disease which makes it an ideal candidate for liver directed gene therapy is that no effective conventional therapy exists for Crigler- Najjar syndrome type I short of liver transplantation. Adenovirus vector mediated gene transfer of a human bilirubin glucuronsyltransferase cDNA (HUG Br 1) is able to transiently reverse the hyperbilirubinemia in Gunn rats. Two general approaches will be used to increase vector efficacy 1) engineer vectors to be less immunogenic and 2) combine vector delivery with pharmacologic immunosuppression. This proposal includes several novel interventions designed to augment expression of the transgene leading to increased efficacy of in vivo adenovirus gene therapy. The experimental design employs multiple modalities to detect gene transfer so that a drop in serum bilirubin may be correlated with other, more specific measures of gene transfer. The results obtained in this model should prove valuable to the development of liver directed gene therapy for other genetic and acquired diseases.